Facing slowing growth for the first time since the iPad’s 2010 debut, Apple is working on several significant software and hardware updates to reinvigorate the tablet over the next year. Apple is developing a dual-app viewing mode, 12-inch iPads codenamed “J98” and “J99,” as well as support for multi-user logins, according to sources briefed on the plans. First planned for debut last year, the split-screen applications feature for the iPad could be introduced as soon as June at Apple’s annual Worldwide Developers Conference, while multi-user login support and the 12-inch iPads will apparently arrive later…